Skin infections in AD patients linked to PMN impairment

Jun 22 2012

By Ingrid Grasmo

Impairment of polymorphonuclear granulocytes (PMN) among patients with atopic dermatitis (AD) may represent an additional cause of skin infections, suggest study findings.

"These data, in addition to the already known keratinocyte membrane disorders, could represent a major contributory cause of infection," say Maria Teresa Fiero (University of Turin, Italy) and colleagues.

"A systematic screening of AD patients could help in identifying a subset of patients particularly susceptible to infections and therefore worthy of closer follow-up or targeted treatment," adds the team.

To investigate functional activity and phenotype of PMN in patients with AD, the researchers evaluated in-vitro PMN phagocytosis and intracellular killing towards Klebisella pneumoniae in 24 AD patients aged 49.3 years on average. Flow cytometry was used to analyze PMN phenotype and results were compared with 15 healthy individuals matched for age and gender.

In total, 19 of the 24 patients had immunoglobulin E levels above 100 kU/L, and were therefore considered as having extrinsic AD, while the remaining five patients were diagnosed with intrinsic AD. Furthermore, 16 patients had eczematous lesions involving over 40% of the skin surface, while eight patients were erythrodermic.

Analysis of PMN functional activity against K. pneumoniae showed that PMN from AD patients had reduced phagocytic activity relative to controls. Indeed, PMN harvested from controls phagocytized the bacteria from 19.1% to 15.5% over a 90-minute incubation period, compared with 15.6% and 12.5% after 30 and 60 minutes among AD patients.

This reduced phagocytic activity was accompanied by a decreased efficiency of PMN in killing the ingested bacteria, with a survival index of 1.69 versus 1.43 for controls after 30 minutes.

Flow cytometry revealed no significant differences between AD patients and healthy controls in the percentage values of CD11b, CD62L, and CD66b. Furthermore, no significant difference was observed in the percentage expression of Toll-like receptor (TLR)-2, 4, 5, 8, or 9 in the PMN from AD patients and healthy controls.

Median fluorescence intensity values were found to be significantly higher in patients with AD for TLR2, TLR4, and TLR5.

Writing in the journal Dermatology, Fiero and co-authors call for a larger patient series including those with limited disease to better clarify whether phenotypical and functional abnormalities are confined to a subgroup of patients with severe disease.

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